Most of the over twenty epidemiologic studies that have examined the relationship between dietary folate intake and the risk of developing colorectal neoplasms, have reported that higher folate intakes are associated with lower risk. Animal studies, using either carcinogen-induced or genetically engineered rodent models of colorectal cancer, have indicated an inverse relationship between dietary folate and the risk of colorectal cancer. The folate metabolic pathway influences genomic methylation and the supply of nucleotides for DNA synthesis; these can also be influenced by adequacy of supply of vitamins B12, B6, and B2, all co-factors for critical enzymatic reactions in the pathway. The overall long-term objective of our Team is to establish the role of folate and other nutritional contributors to one-carbon metabolism in colorectal cancer by combining animal, mechanistic, human observational studies and clinical trials. We will accomplish this by establishing a Cooperative Specialized Center for the study of Folate, One carbon nutrients, Gene variants and Colorectal cancer. This Center will be a Collaborative Program between Harvard and Tufts Universities in Boston, Dartmouth University in New Hampshire, the International Agency for Research in Cancer and the University of Bergen in Europe, Variagenics Inc. in Boston, and the Division of Cancer Prevention and the Center for Cancer Research at the NCI. We are organized into three projects, developmental projects, and two cores. Project 1 will pool data from three large prospective cohort studies with 2,700 expected colorectal cancer cases to establish whether higher intake of folic acid reduces risk of colorectal cancer and examine whether this reduced risk is greater among persons with low methionine intake, low plasma folate, vitamins B12, B6, and B2 levels, consumers of more than one alcoholic beverage per day, and homozygotes for the methylenetetrahydrofolatereductase (MTHFR) C677T polymorphism, and compound heterozygotes for the MTHFR A1298C polymorphism. Project 2 will validate mouse models of colon carcinogenesis as systems to examine modification of risk by folate and other contributors to one-carbon metabolism. Project 3 will assess whether the degree of uracil misincorporation and genomic methylation in peripheral blood lymphocytes and distal colon biopsies represent biomarkers of one-carbon nutrient adequacy and colorectal adenoma risk, using data and samples from two randomized clinical trials of folate supplementation. The projects will be supported by innovative Developmental Projects. In initial Developmental Project 1 transgenic mice with the null allele of MTHFR, and the homologous C677T polymorphism; these mice will be available for incorporation into feeding studies in Project 2. In Developmental Project 2 we will explore five folate-metabolism genes for polymorphisms that influence plasma folate and homocysteine levels. All Projects will be supported by the Administrative and Statistical Core (based at the Harvard School of Public Health), and the Measurement Core (based at the Human Nutrition Research Center at Tufts University). These highly interrelated studies will help integrate epidemiologic and mechanistic observations and help provide a basis for public health recommendations on optimal levels of folate and B vitamin intake.